Lower alkyl esters of L-phenylalanine are preferred starting materials in the manufacture of certain sweetening agents as disclosed in U.S. Pat. No. 3,492,131. However, heretofore those starting materials have been difficult and expensive to obtain. Due to the absence of suitable asymmetric syntheses, prior art efforts have been directed most often to the resolution of the DL-compounds.
Prior art methods have employed resolving agents derived from amino acids different than those being resolved, see for example, Kato and Tsuchiya, Agr. Bio. Chem., Vol. 26, No. 8, 467 and 473 (1962). As an exception, the resolution of the t-butyl ester of DL-phenylalanine employing N-carbobenzoxy-L-phenylalanine as the resolving agent has been reported in Roczniki. Chem., 40 (11/12), 1895 (1966). However, the urethane type carbobenzoxy group employed therein is not desirable because of its potentially dangerous preparation from phosgene and benzyl alcohol. Additonally, from an economic standpoint, it is undesirable to utilize a derivative of L-phenylalanine as resolving agent since its use as starting material for the production of sweetening agents makes it very valuable. Even small losses of resolving agent would result in substantial additional costs.